On the last play of the third quarter in Sunday’s 26-0 win over St. Louis, Grant left a lasting impression on Jackson, stuffing him for no gain with a tackle that had Grant’s helmet flying, his teammates whooping and Fox announcer Tim Ryan saying, prior to a replay of the collision, “Listen to this.”

“When he hit Steven Jackson, it was exciting,” said left tackle Alex Boone, Grant’s teammate for two seasons at Ohio State. “It got the sidelines up. Everyone was excited again.”

Grant played most of Sunday’s game because of a hamstring injury Pro Bowl linebacker Patrick Willis sustained in the first quarter. And it appears Grant will reprise his fill-in role when San Francisco (10-2) visits the Cardinals (5-7) on Sunday. According to ESPN, Willis has a Grade 2 hamstring strain and could miss “a little time.” Hamstring strains are graded on a scale of 1 to 3, with 3 being the most severe.

“Nobody wants to get hurt,” Willis said after Sunday’s game. “But for (Grant) to play the way he did against his former team, that’s phenomenal.”

Indeed, Grant did a fair impression of his Pro Bowl teammate after spending the past three seasons in St. Louis, starting eight games in 2010. Grant shared team-high honors with six tackles, had a sack, two tackles for loss and a quarterback pressure.

Grant, 26, who spent part of his childhood in Hunters Point, attended City College of San Francisco before signing with Ohio State. Boone says Grant, as a junior-college signee, arrived in Columbus with something to prove. Boone noted Grant had a similar “chip on his shoulder” Sunday against St. Louis, which didn’t re-sign him after the lockout.

“It was exciting to see him play so well because that’s something you want to do when a team lets you go,” Boone said. “It’s like ‘Hey, we’re playing them. I want to let them know – you let go of a good player.’ And he did that for us.”

Said Grant, a seventh-round pick of the 49ers who was signed off their practice squad by the Rams as a rookie in 2008: “Of course, it’s a great thing playing against your old team, but I got to keep all the emotions to the side and stay within the scheme of the defense. I had fun. I love everybody in that locker room.”

Prior to getting his most extensive playing time on defense Sunday, Grant had made his mark on special teams. He was named the special-teams captain against St. Louis based on his performance in the previous game, a 16-6 loss at Baltimore.

Harbaugh was first struck by Grant’s physicality on special teams in a 13-8 win at Cincinnati on Sept. 25 when he leveled Brandon Tate on a kickoff return.

“Seeing how fast he could get from point A to point B and make contact with his full body at full speed, full throttle,” the 49ers’ head coach said of the tackle. “… At full speed, it’s a beautiful thing.”